You can go with 2-CPU license or 1-CPU license, if your server serves large amount of static content or https traffic, you'd better go with 2-CPU license.

The trial license is a 2-CPU license. Please check our store for pricing.

After you purchase a license, you will get a email like this

Code:

Dear **** *****,
Thank you for purchasing LiteSpeed software:
LiteSpeed Web Server Enterprise Edition (2 CPU-Core) Monthly Subscription: Expire Date (YYYY-MM-DD) = 2008-09-02.
Your serial number is
"xxxx-xxxx-xxxx-xxxx"
This serial number allows you to install the software on 1 Server .
Please follow the below instructions to obtain a license key.
1) Please save the above serial number, minus quotes, as a file named
"serial.no" in the installation folder: same folder as install.sh.
The installation package can be downloaded from:
[URL="http://www.litespeedtech.com/support/forum/../../products/webserver/download/"]http://www.litespeedtech.com/products/webserver/download/[/URL]
2) Run ./install.sh.
3) Answer the license agreement and select the installation target.
4) Then the installer will check whehter "serial.no" exists in the
same directory. If there is, it will connect to LiteSpeed products
registration server and get a license key file automatically. If
the license key retrieved successfully, the installation will
continue.
5) If the automatic process failed due to whatever reason, the
Installer will leave a license key request file "lic_req.bin" in
the same directory and exit. Please email the license request file
as attachment to [EMAIL="register@litespeedtech.com"]register@litespeedtech.com[/EMAIL] with Subject "New
License Request" for manual process.
6) After a valid license key file named as "license.key" available in
the installation directory, you can run Installer again to continue
installation.

Then you just select "Upgrade", then hit "Enter" all the way to the end. Your current installation will stay the same.